Evolution of Arabic Gum-based green mortar towards enhancing the engineering properties – Fresh, mechanical, and microstructural investigation

Contemporary and innovative construction has propelled the usage of varying types of admixtures to modify its properties in fresh and hardened states. However, the commercially available admixtures pose socio-economic and techno-ecological challenges. Arabic Gum (AG) trees exist widely in sub-tropical / sub-Saharan regions and the production of AG is continuously escalating due to various commercial benefits offered by this emerging class of natural biopolymer. This study aims to synthesize the mortar utilizing AG as a green additive. A control mix and five AG-based mixes were developed by varying the AG content in the range of 0–1.5 % by weight of cement. The flow, setting time, compressive and flexural strengths, and volume of permeable voids were evaluated. The results were also complimented by means of Scanning Electron Microscopy (SEM), Energy Dispersive Spectroscopy (EDS) analysis, Fourier Transform Infrared (FTIR) spectroscopy, and X-ray Diffraction (XRD) analysis. A linear increase in the flow and setting time was observed with an increase in the AG content attributed to lubricating and retarding effects, respectively. However, a dosage of 0.75 % was considered optimum for enhancing the overall engineering properties. This mix achieved a compressive strength of 32.6–52.5 MPa and a flexural strength of 4.3–6.5 MPa between 7 and 56 days, respectively. The increased mechanical characteristics in the range of 12–31 % compared to the control were attributed to the reduction in the volume of permeable voids of mortar up to 19.6 %. The analytical tests revealed a dense microstructure of 0.75 %-admixed AG specimens attributed to the adequate dissolution of the cementitious material intertwined with a low Ca/Si ratio and a weak hydroxyl group in its matrix leading to more formation of C[sbnd]S[sbnd]H gel. It is postulated that the optimum condition of AG can be beneficially exploited in sustainable infrastructural applications as an alternative to conventional admixtures used as superplasticizer, retarder, pore-filling, crack-bridging, and strength enhancing agents.